Seed meters are used by agricultural seeding machines to control the rate at which seed is applied to a field. Air pressure meters use either positive or negative air pressure to direct seed to apertures formed in a rotating seed disk and to hold the seed in the apertures until a preselected release point is reached. Sealing or cut-off structure on the seed meter typically is used to isolate a portion of the rotatable seed disk from the air pressure source so that the seed is released from the apertures. The seed then follows a trajectory away from the disk into a seed tube or the like towards the ground.
Air pressure seed meters commonly utilize plastic seed disks which vary in configuration depending on the type and size of seeds being metered. For example, a vacuum meter may use either a celled seed disk or a flat seed disk installed at a given location on a driven hub. The seed trajectory off the disk in the release area typically varies with the type of seed disk being used. The trajectory off the celled disk tends to be more centered relative to the seed tube entry walls than the trajectory for the flat disk, which is closer to the proximate seed tube wall. If the trajectory for the celled disk is optimized, the seed drop will not be in the optimum location for the flat disk. As a result, the seeds released from the flat disk will be offset more from center and will tend to bounce off of the proximate wall instead of falling towards the desired location within the seed tube. The seed bounce off the proximate wall produces unwanted seed spacing variations. In commonly assigned and copending application Ser. No. 11/273,363 Flat Type Seed Meter Disk with Axially Offset Surface, a flat disk is described wherein apertures are spaced along a circumferential rim offset axially from the remainder of the disk to approximately duplicate the seed release location and characteristics of a cell type seed disk.